Low balanced reactance delta closure for electric arc furnace transformers

ABSTRACT

A low balanced reactance delta closure for a three phase electric arc furnace has delta connected tubular coil collectors mounted close to the transformer. Triangulated tubular phase conductors project through the wall of a closed transformer vault connecting to the collectors inside the vault and to flexible cable terminal heads, spaced for triangulation of the suspended cables, outside the vault. In each phase liquid coolant from an inlet connection outside the vault flows through an inlet passageway inside the tubular conductor, through passageways inside the tubular collector, back through the outlet passageway inside the tubular conductor and to an outlet connection outside the vault.

United States Patent [191 Trageser [451 Aug. 12, 1975 [75] Inventor: James J. Trageser, Pittsburgh, Pa.

[73] Assignee: United States Steel Corporation, Pittsburgh, Pa.

[22] Filed: July 23, 1974 [21] Appl. No.: 491,080

Related US. Application Data [63] Continuation-in-part of Ser. No. 432,918, Jan. 14,

1974, abandoned.

[52] US. Cl 13/12; 336/12 [51] Int. Cl. H05b 7/10 [58] Field of Search 13/12, 13; 336/12 [56] References Cited UNITED STATES PATENTS 1,386,828 8/1921 Winston 336/12 3,366,725 l/l968 Watterson 13/12 Primary ExaminerR. N. Envall, Jr.

Attorney, Agent, or FirmRea C. Helm [5 7] ABSTRACT A low balanced reactance delta closure for a three phase electric arc furnace has delta connected tubular coil collectors mounted close to the transformer. Triangulated tubular phase conductors project through the wall of a closed transformer vault connecting to the collectors inside the vault and to flexible cable terminal heads, spaced for triangulation of the suspended cables, outside the vault. In each phase liquid coolant from an inlet connection outside the vault flows through an inlet passageway inside the tubular conductor, through passageways inside the tubular collector, back through the outlet passageway inside the tubular conductor and to an outlet connection outside the vault.

9 Claims, 12 Drawing Figures FIG. 2.

PATENTEDAum ems 3' 898 7m FIG. 4.

LOW BALANCED REACTANCE DELTA CLOSURE FOR ELECTRIC ARC FURNACE TRANSFORMERS This application, which is a continuation-in-part of my copending application Ser. No. 432,918 filed .Ian. 14, 1974, now abandoned relates to electric arc furnace transformers and more particularly to a low balanced reactance water cooled delta closure for such a transformer.

Three phase electric arc furnaces are used in the process of melting and refining steel. A typical arrangement includes a high voltage power supply connected to a transformer to provide a high current output at a relatively low voltage. The transformer output is delta connected to cable terminal bars, through a group of flexible cables to one end of a group of bus tubes mounted on a movable mast supporting electrode holders over the top of the furnace. The other end of the bus tubes are connected to the furnace electrodes. Because of high currents involved, the flexible tubes and the bus tubes mounted on the mast are water cooled. The flexible cable connection is required to permit movement of the furnace top and tilting of the furnace.

The transformer is usually enclosed in a pressurized protective vault as near the furnace as is convenient and includes a cooling system for the transformer. The power transformer has a plurality of secondary coil terminal blades projecting from the top face of the transformer. Secondary riser extension bars are bolted to the blades and to a series of closure bars, one for each transformer secondary coil terminal, which are in turn bolted to the three cable terminal bars. The cable terminal bars project through the wall of the vault with the closure bars inside the vault and the cable connections outside the vault. In large capacity transformers there may be as many as seventy-two or ninety-six air cooled closure bars converging diagonally from the risers to the cable terminal bars. Each closure bar may be in two parallel sections with spacers between the sections. This type of closure requires a complex series of support timbers and comb spacers for the closure bars.

The transformer vault is usually sealed and provided with a positive air pressure to prevent entrance of dirt which can accumulate on the closure bars and supporting structure and cause flashovers. The flow of filtered air also serves to cool the transformer and the structure in the vault, and if desired, the air may be cooled before entry into the vault.

For efficient furnace operation it is important that the impedance in the electrical circuit from the transformer to the electrodes be balanced between the three phases and also be as small as possible. Impedance unbalance is caused by different conductor length and unbalanced spacial relationships between the three conductors. The impedance unbalance becomes even more important with the trend towards higher currents, while a typical I50 ton furnace operated at 40,000 amperes a few years ago, 150 ton furnaces now operate at about 80,000 amperes. Such high currents create considerable heating problems and conductor support problems as heated copper bars tend to char supporting timbers.

In accordance with my invention I provide a delta closure for a transformer having relatively short riser extension bars bolted to riser extension bar brackets. The brackets are welded to water cooled tubular coil collectors which are in turn welded to water cooled tubular phase conductors projecting through the transformer vault wall and ending with the flexible cable terminals. The phase collectors and the flexible cable terminal heads are supported by hanger rods, and the spacing of the water cooled tubular phase conductors permits maximum reactance balancing to compensate for imbalance in the flexible cables and electrode bus bars. Water cooling is connected to the flexible cableelectrode bus bar cooling system with no connections inside the vault.

It is therefore an object of my invention to provide a delta closure for an electric arc furnace transformer with low, balanced reactance.

Another object is to provide such a closure that is liq uid cooled.

A still further object is to provide such a closure which is easily supported by hanger rods yet another object is to provide such a closure having no coolant connections inside the transformer vault.

These and other objects will become more apparent after referring tothe following specifications and drawings in which:

FIG. 1 is a schematic elevation, partially in section, of an electric arc furnace installation with the delta closure of my invention,

FIG. 2 is a schematic plan view, partially in section, of an electric arc furnace installation, with the delta closure of my invention,

FIG. 3 is a schematic side elevation of the delta closure assembly,

FIG. 4 is a schematic front elevation of the delta closure assembly,

FIG. 5 is a schematic plan view of the delta closure assembly,

FIG. 6 is a sectional detail of the connection between the tubular coil collector and riser tubes of phase A.

FIG. 7 is a cross sectional view along line VII-VII of FIG. 5 showing the coolant connections of phase A.

FIG. 8 is a sectional detail of the connection between the tubular coil collector and the tubular phase conductor of phase C.

FIG. 9 is a cross sectional view along line IX--IX of FIG. 5 showing the coolant connections of phase C.

FIG. 10 is sectional detail of the connection between the tubular coil collector and the riser tubes of phase C.

FIG. 11 is a cross sectional view along line XIXI of FIG. 5 showing the coolant connections and stiffeners of phase B.

FIG. 12 is a cross sectional view along line XII-XII of FIG. 5 showing stiffener details.

Referring now to FIGS. 1 and 2, a typical three phase electric furnace installation includes a large cylindrical furnace housing 2, upon which rests a movable roof 4. Electrodes 6 project downward through the roof 4 and are supported by electrode holders mounted on a mast assembly 8 which also supports bus tubes 10. Bus tubes 10 are usually water cooled and are connected at one end to the holders for electrodes 6 and at the other end to mast cable terminal heads 12. Flexible water cooled cables 14 are connected from the mast cable terminal heads 12 to the transformer cable terminal heads 16. Terminal heads 16 are connected through the closure system of my invention to a power transformer 18. Transformer 18 is enclosed in a vault 20, only a pan of which is shown, and is connected to a source of high voltage three phase alternating current 22. A cooling system 24, partially shown in FIG. 2, is provided to cool vault 20. Transformer 18 provides a high current low voltage output and is usually provided with a cooling system, not shown. The parts thus far described, with the exception of the closure system, are conventional.

Referring now to FIGS. 3, 4 and 5, showing the delta closure assembly of my invention, reference numeral 26 indicates a plurality of transformer secondary coil terminal blades rising from the top of the transformer 18. The terminal blades 26 as shown in FIG. 4 are in three groups, with the ends of each secondary coil connected to a pair of adjacent blades. Bolts 28 affix a pair of terminal riser bars 30 to each terminal blade 26. A riser extension bar 32 is affixed to the top of each pair of terminal riser bars 30 by bolts 34. The designation of the riser extension bars is shown in FIG. 3 as 32A for phase A, 328 for phase B and 32C for phase C.

Each riser extension bar is welded to a tubular coil or phase collector 36 which may be, for example, a square hard drawn high conductivity copper tube 8 inches square with /2 inch wall thickness. Each phase collector has three or more vertical support hanger lugs 38, as best shown in FIG. 5. The hanger lugs are connected by hanger rod assemblies 40 which include turnbuckles, eyebolts, rods, clevis and an insulator 42, to roof beams 44 of transformer vault 20. For clarity, only a portion of the support rods 40 and roof beams 44 are shown. The ends of each tubular collector 36 are closed by end caps 46.

A pair of hollow riser tubes 48A is welded to phase collector 36A. Riser tubes 48A may be, for example, hard drawn high conductivity copper tubes six inches square with /2 inch wall thickness. A pair of hollow riser tubes, 488, similar to riser tubes 48A, is welded to phase collector 363. A tubular phase conductor is made of two tubes 50B, is welded to the ends of riser tubes 48B and projects through vault wall 52. Supporting and insulating timbers 54 surround tubes 50B for a snug fit through an opening in vault wall 52. Another tubular phase conductor is made of two tubes 50A, is welded to the end of riser tubes 48A and projects through vault wall 52 in the same manner as tubes 50B. A third phase conductor is made of two tubes 50C, is welded to phase collector 36C and likewise projects through vault wall 52. Tubes 50A, 50B and 50C may each be, for example, hard drawn high conductivity copper tubes siz inches square with /2 inch wall thickness.

A pair of terminal heads 56 is welded on the end of each phase conductor. Hanger rod assemblies 58A and 58C shown in FIG. 3 and partially in FIG. 4 and similar to hanger rod assemblies 40, are attached to terminal heads 56A and 56C and a roof beam 44, shown in FIG. 3, projecting outside of vault 20. A pair of hanger rod assemblies 588, similar to hanger rod assemblies 40, are attached to terminal head 56B and extend diagonally to outer roof beams 44 projecting outside vault 20. For clarity, FIG. 3 shows only a portion of the hanger rod assembly 58B and FIG. 4 Shows only a portion of one of the hanger rod assemblies 588. Cables 14 are equipped with lugs which are bolted to terminal heads 56. The ends of tubes 50 to which terminal heads 56 are attached have end caps 60 welded in place.

Referring now to FIG. 6, phase collector 36A has a diagonal coolant separator 62A inserted inside it extending almost the entire length of collector 36A as shown in FIG. 5. Separator 62A may be /2 inch thick hard drawn high conductivity copper. A hole 64 passes coolant from the upper right half of collector 36A into the outlet riser tube 48A, and matching holes 66 in collector 36A and inlet riser tube 48A passes coolant from the inlet riser tube 48A to the lower left half of collector 36A. A cap 68, welded in place, covers the end of inlet riser tube 48A and a spacer 70 separates riser tubes 48A between the connection to collector 36A and the connection to the phase conductor 50A. In FIG. 7 a coolant inlet 72A is connected to the lower inlet tube 50A and a coolant outlet 74A is connected to the upper tube 50A. An air bleeder plug 76A is provided in the lower outlet tube 50A. Drain plugs 78A are provided at each end on the bottom side of phase collector 36A as shown in FIG. 5.

Referring now to FIG. 8, phase collector 36C has a diagonal coolant separator 62C inserted inside it extending almost the entire length of the collector as shown in FIG. 5. Separator 62C may be inch thick hard drawn high conductivity copper. Matching holes 80 through the wall of the collector 36C and the upper outlet tube 50C passes coolant from the upper right half of collector 36C into upper outlet tube 50C. A hole 82 in the wall of collector 36C passes coolant from the lower inlet tube 50C into the lower left half of collector 36C. A cap 84 welded in place covers the end of upper outlet tube 50C. In FIG. 9, a coolant inlet 72C is connected to the lower inlet tube 50C and a coolant outlet 74C is connected to the upper outlet tube 50C. An air bleeder plug 76C is provided in the lower inlet tube 50C. Drain plugs 78C are provided at each end on the bottom side of phase collector 36C as shown in FIG. 5.

Referring now to FIG. 10, phase collector 363 has a diagonal coolant separator 62B inserted inside it extending almost the entire length of collector 36B as shown in FIG. 5. Separator 62B may be /2 inch thick hard drawn high conductivity copper. A hole 86 in collector 36B passes coolant from inlet riser tube 48B into the upper left half of collector 36B, and matching holes 88 in collector 36B and outlet riser tube 488 passes coolant from the lower right half of collector 368 to outlet tube 48B. A cap 90, welded in place, covers the end of the inlet tube 488. A spacer 92 separates riser tubes 488 between the connection to collector 36B and the connection to the tubes 503. In FIG. 11, a coolant inlet 72B is connected to the lower inlet tube 50B and a coolant outlet 74B is connected to the upper outlet tube 508. An air bleeder plug 768 is provided in the lower inlet tube 508. Drain plugs 78B are provided at each end on the bottom side of phase collector 368 as shown in FIG. 5.

Collectors 36, risers 48 and conductors 50 may be single tubes with interior spacers to define coolant passageways or tube pairs as shown, whichever may be structurally convenient. If the phase collector is constructed with more than one tube, it may be arranged with either a single coolant flow path looping throughout the entire length of the collector, or multiple coolant flow paths, such as separate coolant flow paths looping on either side of the connection with the phase conductor. In the latter case, there may be two separate flow paths in each phase which may be arranged either in series or in parallel in the overall coolant flow system.

The length of tubes 50B may be so long that stiffeners are required. FIGS. I1 and 12 show a preferred stiffener in one of the tubes, other stiffeners may be used or stiffeners may be used in both tubes. In FIGS; 5, 11 and 12, the stiffener consists of a stainless steel tube 94, sealed at both ends. Four corner spacers, 96, are welded to tube 94 so that the tube and spacer assembly fits snugly inside lower inlet tube 50B. Tube 94 extends from nearly one end of tube 508 to the other end as shown in FIG. 5. The spacers 96 may conveniently extend about the same distance. This configuration of the stiffener provides four sub-passageways for coolant through the stiffened tube 50B. In FIG. 12-, a baffle 98 is placed in the lower quadrant passage so that the entering coolant will be forced into other passageways.

Since large capacity electric arc furnaces require a cooling system for cooling of the flexible cables, the bus tubes connected to the electrodes'and the electrode holders it is convenient to use the same cooling system or part of the system for the delta closure of my invention. Referring now to FIG. 3, reference numeral 100 indicates a coolantsupply header which may be conveniently mounted on vault wall 52. Header 100 is connected to a source of coolant, not shown. The source may be a pumpsupplying cool water or other coolant under pressure from a cooling tower, coolant tank, cooling pond or whatever may be convenient for the particular furnace installation. A flexible rubber hose 102 connects the supply header to coolant inlet 72C. Coolant flows through inlet tube 50C, through hole 82, FIG. 8, into the lower left half of collector 36C. The coolant flow then divides, part going to each end of collector 36C. The coolant then passes around the ends of spacer 62C into the upper right half of collector 36C, back to the middle of collector 36C and through matching holes 80 to upper tube 50C. The coolant leaves through coolant outlet 74C. Coolant flow in phases A and B are similar except that coolant also passes through riser tubes 48A and 488.

A flexible rubber hose 104 connects outlet 74C to an inlet connection 106 on the transformer cable terminal head 56. Coolant flows through one of the flexible cables 14, through connections 108 at the mast cable terminal head 12 back through a second flexible cable 14, an outlet connection 1 C, and a flexible hose 112C to a discharge header 114. Header 114 may be conveniently mouted on vault wall 52 and is appropriately connected to the cooling system as already described.

The delta closure of my invention permits a considerable reduction in the cooling required for the transformer vault, in fact, the normal transformer cooling system and the delta closure cooling system can be adequate without vault cooling. Maximum use of welding in the closure structure reduces maintenance and improves the conductivity of the closure. The water cooling of the closure can be readily connected to other cooling systems, safety is assured because all connections to the cooling system are outside of the transformer vault. The structure permits a minimum connection from the transformer blades to the cable terminals; and also permits use of more secondary coils than the prior type of delta closure. Maintenance of the hanger system is considerably improved because the timber and spacer system has been replaced by simple hanger rods.

By gathering the transformer coil ends to the phase collectors as close as possible to the transformer tank, the reactance is considerably lower than the reactance in the conventional system using diagonally converging closure bars. In addition, the triangular spatial relation of the phase conductor tubes as they project through the transformer vault wall also contribute to a lower reactance. The conductors are terminated outside the vault wall to provide a triangular spatial relation to the flexible cables.

The closure also tends to balance reactances to eliminate undesirable hot and cold phases occurring when conductor systems are not triangulated. As long as the flexible cables and the bus tubes are also arranged in a triangular spatial relation, the triangular spatial relation of the phase conductors completes a triangular pattern for the entire conductor system leaving only uncontrollable operating conditions within the furnace itself to contribute towards the imbalance that results in hot and cold phases. The spatial relationship may also be varied to compensate for undesirable reactance imbalance elsewhere in the system and thus the closure may act as a balancing reactance. Likewise, a phase conductor length may be varied with respect to other phase conductors to overcome undesirable impedance imbalances in the system. For example, if the triangular arrangements of the electrodes as shown in FIG. 2 were rearranged so that the center or B phase electrode was closer to the transformer than the other electrodes, the overall conductor length of all phases could be made more nearly equal since the phase conductor in phase B is longer than the phase conductors of the other two phases as seen from FIGS. 1 and 3.

While I have described several embodiments of my invention, it is apparent that other modifications may be made.

I claim:

1. In a three phase electric arc furnace, a low balanced reactance delta closure connecting a power transformer to flexible cables comprising a row of secondary coil terminal blades projecting from a face of the transformer;

a plurality of terminal risers, one of each of said risers being connected to each terminal blade;

a tubular phase collector for each phase, said collectors being arranged generally parallel to said row of blades and delta connected to said risers;

a tubular phase conductor for each phase, said conductors being arranged generally parallel to each other and in a triangular spatial relation, each of said phase conductors having means connecting one end thereof to one of said phase collectors and;

a flexible cable terminal head for each phase mounted on the other end of each of said phase conductors, said other ends being terminated to provide a generally triangular spacial relation for the flexible cables connected to said terminal heads.

2. A closure according to claim 1 which includes a coolant inlet on each tubular phase conductor adjacent the cable terminal head and a coolant outlet on each tubular phase conductor adjacent the cable terminal head and wherein the connection between each tubular phase conductor and its associated tubular phase collector provides a coolant flow path from the coolant inlet through the tubular phase conductor and the tubular phase collector to the coolant outlet.

3. A closure according to claim 2 in which each tubular phase collector is a tube having a cap closing each end of the tube and the coolant flow path includes means inside the tube for dividing the interior of the tube into a pair of coolant passageways, said means for dividing terminating near each end of the tube thereby providing a connection between passageways at each end of the tube,

and in which each tubular phase conductor includes a cap closing the end of the conductor adjacent the cable terminal head and with said conductor being divided inside into an inlet passageway and an outlet passageway for providing the coolant flow path, each of said passageways being connected respectively to one of the passageways in said collector tube.

4. A closure according to claim 2 in which the coolant flow path includes a plurality of interior passageways inside each tubular phase conductor connected to a plurality of passageways inside the associated tubular phase collector.

5. A closure according to claim 2 in which the flexible cables are hollow for coolant flow and which includes a coolant supply header and a coolant discharge header located near said flexible cable terminal heads and a coolant flow path for each phase from the supply header through a flexible cable in the direction of transformer to furnace, through another flexible cable in the direction of furnace to transformer, into the coolant inlet, and from the coolant outlet to the discharge header.

6. A closure according to claim 3 which includes means within a passageway inside a tubular phase conductor for stiffening the conductor.

7. A closure according to claim 6 in which said means for stiffening creates sub-passageways within the conductor and which includes means for directing the coolant flow into said sub-passageways.

8. A closure according to claim 2 which includes a closed transformer vault, insulating means in a wall of said vault surrounding said phase conductors where they pass through the wall in the triangular spatial relation, means inside said vault and attached to said vault for supporting the phase collectors and means outside said vault and attached to said vault for supporting th flexible cable terminal heads.

9. A closure according to claim 3 in which the connections of the risers to the phase collectors, the phase collectors to the phase conductors and the end caps of the collectors and conductors are welded. 

1. In a three phase electric arc furnace, a low balanced reactance delta closure connecting a power transformer to flexible cables comprising a row of secondary coil terminal blades projecting from a face of the transformer; a plurality of terminal risers, one of each of said risers being connected to each terminal blade; a tubular phase collector for each phase, said collectors being arranged generally parallel to said row of blades and delta connected to said risers; a tubular phase conductor for each phase, said conductors being arranged generally parallel to each other and in a triangular spatial relation, each of said phase conductors having means connecting one end thereof to one of said phase collectors and; a flexible cable terminal head for each phase mounted on the other end of each of said phase conductors, said other ends being terminated to provide a generally triangular spacial relation for the flexible cables connected to said terminal heads.
 2. A closure according to claim 1 which includes a coolant inlet on each tubular phase conductor adjacent the cable terminal head and a coolant outlet on each tubular phase conductor adjacent the cable terminal head and wherein the connection between each tubular phase conductor and its associated tubular phase collector provides a coolant flow path from the coolant inlet through the tubular phase conductor and the tubular phase collector to the coolant outlet.
 3. A closure according to claim 2 in which each tubular phase collector is a tube having a cap closing each end of the tube and the coolant flow path includes means inside the tube for dividing the interior of the tube into a pair of coolant passageways, said means for dividing terminating near each end of the tube thereby providing a connection between passageways at each end of the tube, and in which each tubular phase conductor includes a cap closing the end of the conductor adjacent the cable terminal head and with said conductor being divided inside into an inlet passageway and an outlet passageway for providing the coolant flow path, each of said passageways being connected respectively to one of the passageways in said collector tube.
 4. A closure according to claim 2 in which the coolant flow path includes a plurality of interior passageways inside each tubular phase conductor connected to a plurality of passageways inside the associated tubular phase collector.
 5. A closure according to claim 2 in which the flexible cables are hollow for coolant flow and which includes a coolant supply header and a coolant discharge header located near said flexible cable terminal heads and a coolant flow path for each phase from the supply header through a flexible cable in the direction of transformer to furnace, through another flexible cable in the direction of furnace to transformer, into the coolant inlet, and from the coolant outlet to the discharge header.
 6. A closure according to claim 3 which includes means within a passageway inside a tubular phase conductor for stiffening the conductor.
 7. A closure according to claim 6 in which said means for stiffening creates sub-passageways within the conductor and which includes means for directing the coolant flow into said sub-passageways.
 8. A closure according to claim 2 which includes a closed transformer vault, insulating means in a wall of said vault surrounding said phase conductors where they pass through the wall in the triangular spatial relation, means inside said vault and attached to said vault for supporting the phase collectors and means outside said vault and attached to said vault for supporting the flexible cable tErminal heads.
 9. A closure according to claim 3 in which the connections of the risers to the phase collectors, the phase collectors to the phase conductors and the end caps of the collectors and conductors are welded. 